Beeing the owner of my ZEN for only a few days now, I bought a new set of tubes for it here in Holland since I have no clue how old [ worn] the tubes are that came with it. All tubes[ types recommended by Steve]are perfect but one....Problem is; the 5U4G rectifier tube does not fit because it is too thick; it touches the transformer.It has the 5Y3G now, and I thought the 5U4G was the correct one for this amp..Please point out my misstake?Thanks,Nico

Re: 5U4G; I must have missed something...Reply #5 - 08/09/11 at 07:29:47

AHHH....that explains, thanks.The one I bought is wider at the top so that will be the issue. The space between transformer and rectifier is VERY SMALL....After looking at the transformer-"feet" I noticed that the screws are both in the "most inner position" of the long holes.Drilling two holes further to the back would make it possible to move the transformer significantly more to the back side. The two existing holes would dissappear under the transformer, making them invisible. I'll unscrew the four screws and check if the wires will permit doing so first.Will be back with the result, thanks for your support.Nico

Re: 5U4G; I must have missed something...Reply #6 - 08/09/11 at 21:33:24

Things are falling into place today.As strange as it was to find no serialnumber on this amp, what I found out today is strange even more.After buying a 5U4G [the amp came with a 5Y3G] I found out qiuck enough this rectifier would never fit....The glass was simply too thick for the small space between transformer and socket.I just found out the transformer was not mounted correctly. The two bolts on the rectifier-side were not mounted in the threads that are inserted in the housing; new holes are drilled more to the front.I noticed these two bolts to sit not upright, but under an angle; caused by the threaded inserts.After unscrewing all four screws the transformer could be moved enough to the rear to use the threaded inserts on the side of the connectors.Now the transformer is sitting more to the back, and the 5U4G fits easily.The person that has assembled this amp was......tired? It makes my earlier suspicion that this amp was sold as a kit a fact.Thanks for your thoughts, at this moment the 5U4G glowes softly and makes an even better-looking amp; now it's time to listen and getting myself to go to bed on time, gonna be hard again. Nico

Re: 5U4G; I must have missed something...Reply #8 - 08/10/11 at 16:29:30

Well, I know for sure that nobody at Decware should mount the transformer that way!The transformer-feet are just too wide apart for using the four threaded inserts in the housing, so either this transformer is not the original, or the inserts are not mounted in the right position.This will remain a mistery I guess, but I'm happy the 5U4G fits now!

Re: 5U4G; I must have missed something...Reply #10 - 09/07/11 at 15:54:43

Bill, either you or someone else previously suggested the black-plate Svetlana NOS rectifiers. I picked up a half dozen from the 50s, and I agree, they are quite nice. Right now, they are back-ups to the RCA NOS black plates I am using, as well as one Raytheon and one Mullard G37, but having listened to them, I feel comfortable they will serve me well when I, or my children, pop them in.

Re: 5U4G; I must have missed something...Reply #11 - 09/07/11 at 16:54:29

Thanks for all the info. Beeing new in tube-land I never thought the rectifier would make such a big difference. At the moment I'm using a CV593 and a GZ32 [basically the same Mullard tube] and the amp performs better with these than the Sovtek 5U4G I bought earlier.The used Mullard GZ32 has the most "liquid" sound, where the CV593 has more dynamics.I must be carefull though.....or I'll end up owning more tubes than I'll ever need in my lifetime [prob. like most of you guys] Nico

Re: 5U4G; I must have missed something...Reply #12 - 11/21/13 at 15:16:00

ok. I have not been around for a while so I need some help here. I have the C version , and that came with the 5y3, but now I see the gz32 and 5u4 being mentioned. Has there been any modifications to the amp or can I just throw in a 5u4 to the 84c.